In order to make a photographic exposure with a camera, a camera housing is provided with an exposure aperture through which light can pass to expose film in the camera. A shutter blade normally closes this aperture to prevent the undesired entry of light through the aperture. The shutter blade is actuated by a shutter mechanism to open the aperture for a predetermined period of time to admit light through the aperture. The shutter mechanism must operate to a high degree of accuracy and reliability if the film is to be exposed properly. Not only must the aperture be opened for the correct total amount of time for proper exposure, but the movement of the shutter blade must be such that this exposure is uniform across the entire area of the film. For example, a shutter blade which sticks or drags slightly across part of its stroke can result in parts of the same film exposure being overexposed and underexposed (known as "shadowing" in the art), even when the average amount of light striking the film over the exposure time is within proper limits.
The necessity for a carefully controlled shutter operation exists in simple, inexpensive cameras as well as in the more sophisticated cameras, and the designer of the simple camera must provide an uncomplicated but accurate and reliable shutter mechanism if the costs of manufacture are to be minimized.
A type of a shutter mechanism commonly used on lower priced cameras includes a pivotable shutter blade which is mounted on a post. The shutter blade pivots between two positions--an aperture closed position and an aperture open position. Such shutters are of the "impact" variety, and are pivotable in response to the release of a spring driven finger which strikes a short lever on one side of the shutter blade to pivot it momentarily into the open position. A return spring is used to bias the shutter blade towards the closed position.
Japanese laid open patent application (Kokai) No. 6-82976 discloses a shutter mechanism of the "impact" variety. Here, a drive mechanism that includes a high energy lever (HEL) strikes a lever on one end of the shutter forcing the shutter blade to pivot into the open position. The high energy lever (HEL) is formed from an arm connected at one end to a finger for striking the lever on one side of the shutter blades. The opposite end of the arm is connected to a bushing rotatably mounted onto a post. The bushing is spring loaded via a torsion spring. When the torsion spring is released by pushing the shutter button, the finger of the HEL sweeps across an arc that strikes the lever of the shutter blade.
While the mechanism disclosed in the '976 patent application is capable of performing its intended function, the inventors have observed several shortcomings in its design that can lead to operational unreliabilities. For example, because the finger of the HEL is supported by a lens mounting plate which is separately installed onto the body of the camera during manufacture, these two parts must be assembled with a high degree of precision if the HEL is to be effectively supported in its proper position throughout its arcuate stroke. Because the arm and the finger of the HEL are relatively long and formed from flexible plastic materials, their cumulative manufacturing tolerances and the manufacturing tolerances on the lens plate may result in a positioning of the finger of the HEL slightly higher or lower than its intended position, resulting again in either no support or excessive friction. Worse yet, the manufacturing and assembly tolerances may add up to the extent where the finger of the HEL sweeps over the lever of the shutter blades without striking it. In such as case, the shutter will not open and the picture will be missed. Finally, the use of the lens mounting plate to provide stability and support of the HEL can create vibrations in the plate that can transfer to the lens during the picture taking operation, thereby degrading the quality of the resulting image.
Of course, these problems could be solved by increasing the accuracy of parts and assembly, but such a solution would increase the cost of the camera.
Clearly, there is a need for an HEL design which enhances the reliability and accuracy of the shutter of a simple, inexpensive camera without significantly increasing the need for parts of tighter tolerances and the consequent increase of manufacture. Ideally, such an HEL design should enhance the performance of the camera as a whole, while simplifying its structure and assembly costs.